The position of an intra-body probe, such as a catheter, can be tracked in the body of a patient using magnetic position tracking techniques. For example, U.S. Patent Application 2007/0265526, whose disclosure is incorporated herein by reference, describes a magnetic position tracking system for performing a medical procedure on a patient. The patient is positioned on an upper surface of a table includes a location pad, which is positioned on the upper surface of the table beneath the patient. The location pad includes one or more field generators, which are operative to generate respective magnetic fields and are arranged so that a thickness dimension of the location pad is no greater than 3 centimeters. A position sensor is fixed to an invasive medical device for insertion into a body of the patient, and is arranged to sense the magnetic fields so as to measure a position of the medical device in the body.
Magnetic resonance imaging (MRI) is an imaging technique used for visualizing tissue, particularly soft tissue, of a patient. The technique relies on exciting nuclei, typically hydrogen nuclei, from their equilibrium state, and measuring the resonant radio-frequency signals emitted by the nuclei as they relax back to equilibrium. The measured resonant radio-frequency signals are used to create high quality images of the tissue. Medical practitioners may use MRI in conjunction with other medical procedures.